The Third Generation Partnership Project (3GPP), one of the standard organizations, has almost completed the standardization of 3GPP Long Term Evolution (LTE) Rel-10 (the system hereafter is also referred to as LTE Advanced (LTE-A)), one of the fourth-generation mobile communication systems, and the standardization of LTE Rel-11, an extended version of LTE Rel-10, has currently been under development.
For uplink (communication from user equipment to a base station apparatus) in these systems, Single Carrier Frequency Division Multiple Access (SC-FDMA) is employed. In the Single Carrier Frequency Division Multiple Access, a frequency signal that is DFT-spread is generated by performing discrete Fourier transform (DFT) on a transmit signal. Moreover, the DFT-spread frequency signals are arranged in an arbitrary frequency resource (also called a subcarrier or a resource block (RB)), contiguously in a frequency direction. Furthermore, the DFT-spread frequency signal is divided into a maximum of two clusters, and clustered DFT-Spread Orthogonal Frequency Division Multiple Access (DFT-SOFDMA) is also employed in which each cluster is arranged in an arbitrary frequency resource in a non-contiguous manner.
Moreover, in PTL 1, a frequency-overlapped access as one non-orthogonal access is disclosed that is based on Spectrum-Overlapped Resource Management (SORM) in which at least some of the DFT-spread frequency signals are allowed to be received in an overlapping manner when received in the base station apparatus and thus the frequency resource is allocated to multiple pieces of user equipment that connect to the base station apparatus at the same time. In PTL 1, a basic configuration of the user equipment and the base station apparatus is disclosed, and particularly, a method of detecting overlapping receive signals based on turbo equalization, and the like are included.
On the other hand, in PTL 2, a method is disclosed in which the allocation is performed for the user equipment with the SORM as a necessary antecedent. In PTL 2, the frequency resource is allocated to each of the pieces of user equipment based on Frequency Division Multiple Access (FDMA) and then multiplexing is performed in the user equipment within a range of an allowable overlap rate. Accordingly, the SORM can be realized without an error rate of the transmit signal deteriorating.